Preheat oven to 450 degrees Fahrenheit. Spray four 6-oz ramekins with cooking spray. Set aside.
Melt chocolate chips and butter inside of a large glass measuring cup with a spout for 30-second increments until melted and smooth.
Add vanilla and salt. Stir. Mix in eggs and egg yolks with a fork. Then mix in the flour.
Pour the batter into prepared ramekins, about 2/3 full.
Place ramekins on a sheet tray and bake at 450˚F for 8-10 minutes. (NO LONGER!) The lava cakes are done when the edges are set, but the middle is still sunken.
Carefully invert cakes onto serving plates immediately. Dust with powdered sugar and serve with fresh raspberries or a scoop of vanilla ice cream.
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Notes
To make ahead: Cover the filled ramekins with plastic wrap or foil and refrigerate until ready to bake. The batter can be made one day ahead of time.
If you don’t have ramekins, you can use a muffin pan. Be sure to grease the muffin pan cups to prevent the cakes from sticking. Since your lava cakes will be slightly smaller, you’ll get 6 lava cakes instead of 4 and the bake time will be less due to the smaller size. Start checking doneness at 4 minutes. Use a spoon to release the cakes from the pan and place each upside down on plates for serving.
How to Invert the Cakes: Place a ramekin on a heat-safe plate. Place another heat-safe plate on top and flip it over while squeezing the two plates together, so the ramekin doesn’t slide. Remove the plate on top and carefully lift the ramekin off of the cake with a hot pad.
To re-heat: Put the cake in the microwave or 20-30 seconds (depending on the power of your microwave) to have a deliciously reheated dessert. It just won’t be as gooey in the center.